Cruise control allows a vehicle to automatically maintain a pre-set speed regardless of gradient. Autonomous cruise control uses laser or radar based devices to allow one vehicle to automatically follow another at a predetermined separation. The invention disclosed herein is not concerned with the general means of autonomous cruise control, and is applicable to many such systems. Autonomous cruise control is typically used in high speed, highway driving, and may be inhibited below a pre-set minimum speed of, for example 30 kph.
‘Queue assist’ is a term applied to low speed autonomous cruise control, such as in an urban environment or highway queuing.
Provision of a queue assist function in vehicles is difficult owing to the need to maintain a relatively small distance between vehicles and the frequency of speed variation. Too large a distance in a congested urban environment allows other road users to enter the space ahead of the following vehicle, and speed variation may be across the entire range of an urban speed limit—from say 0 to 64 kph; such conditions are not common in highway driving where speed variation may be not greater than 20% of the maximum permissible.
Furthermore in highway driving the frequency of events which may interrupt autonomous cruise control is relatively low compared with an urban environment, and for this reason autonomous cruise control may be enabled only above a speed threshold of for example about 30 kph.
In an off-highway environment, a group of vehicles may comprise an experienced lead driver, and novice followers. Queue assist would be desirable so as to maintain vehicle progress whilst allowing novice drivers to concentrate on other tasks, such as steering. Vehicles adapted for off-highway use may include adaptive systems for recognizing the terrain being crossed, and automatically placing the vehicle in a suitable traction mode; this facilitates close following of vehicles in difficult terrain conditions, provided that a queue assist function can be provided.
Conventional protocols for autonomous cruise control specify maximum rates of acceleration and deceleration of the following vehicle. The provide for comfort and security of the occupants of the following vehicle. The driver of the following vehicle may of course manually override these pre-set rates if desired, and other vehicle systems may also be relied upon, such as collision avoidance systems.
If in cruise control mode, the following vehicle will attempt to catch up the lead vehicle at the prescribed rate until the separation distance is at the predetermined value. This means that the following vehicle will travel faster than the lead vehicle from time to time to reduce a separation distance. If the lead vehicle reduces speed, the following vehicle will also reduce speed to maintain an appropriate separation distance.
With a conventional approach, for highway driving, this strategy is appropriate. However in an urban or off-highway environment a lead vehicle may dramatically reduce speed for an obstruction, for example a road hump or ditch, and subsequently increase speed to a safe value. The following vehicle will also reduce speed, and accelerate in unison with the lead vehicle. This may mean that the following vehicle reaches the obstruction at a higher speed than is desirable.
Embodiments of the invention may provide an apparatus, a method or a vehicle which addresses one or more the above problems. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.